Here's link to an article that should give you an unbiased assessment of several units available today:
http://www.fmcmagazine.com/back-issues/2012/july-59795/2887-power-protection.html
We were on the fence as to which one to buy a few years ago. Fortunately at the time Technology Research Corp was introducing some new models. Our local Camping World was liquidating the older models at fire sale prices. We were able to pick up the Surge Guard 34650 hardwired version for $89.00
It does protect against power surges, and both high and low voltage. The big difference is that it has to be sent back to the factory for repairs. However in our case the price was the determining factor.